In the processing of integrated circuits, electrical contact is typically made to isolated active device regions formed within a wafer substrate typically comprising monocrystalline silicon. The active regions are typically connected by high electrically conductive paths or lines which are fabricated above an insulative material formed over the substrate surface. Further, electrical contact is also typically made to other conductive regions received outwardly of the wafer, such as to conductive lines, contact plugs and other devices. To provide electrical connection between two conductive regions, an opening in an insulative layer is typically etched to the desired regions to enable subsequently formed conductive films to make electrical connection with such regions.
The drive for integrated circuits of greater complexity, performance and reduced size has driven designers to shrink the size of devices in the horizontal plane. Yet to avoid excessive current density, the horizontal scaling has not necessarily been accompanied by a reduction in the vertical dimension. This has resulted in an increase of the ratio of device height to device width, something generally referred to as aspect ratio, and particularly with respect to contact openings.
Increased aspect ratio can result in difficulties in the overall etching process typically used to etch openings through insulative materials for making an electrical contact. For example, one common insulating material within or through which electrical contact openings are etched is borophosphosilicate glass (BPSG). A typical process for etching a contact opening in such material includes dry anisotropic etching, with or without plasma. The ever increasing aspect ratios of contact openings has been accompanied by undesired deposits or residue remaining behind on the sidewalls or base of the contact openings at the conclusion of the etch. This residue is typically in the form of a tenacious and insulative carbon polymer derived from one or both of photoresist which is undesirably removed during the etch or the etching gases themselves used to etch the contact opening through the insulator. The insulative residue at best reduces the contact area available for the desired region to which electrical connection is to be made. At worst, it can completely occlude subsequently deposited conductive material from making suitable electrical contact with the desired region. Residue material might also be present in the form of native silicon dioxide and sub-stoichiometric oxide. Such can by themselves increase contact resistance, particularly with sub-stoichiometric oxide which adversely affects silicidation when forming silicide contacts.
While the invention was principally motivated and resulted from achieving solutions to the above-identified problems, the invention is not so limited, with the scope being defined by the accompanying claims as literally worded and interpreted in accordance with the Doctrine of Equivalents.